In hydraulic construction machinery such as an excavator, working machines and a top swing body are operated by working oil discharged from a pump operated by an engine. In more detail, a flow direction of the working oil discharged from the pump is controlled by a control valve switched according to a signal pressure generated from an operation unit and thus, the working oil is supplied to each working machine and a swing motor. The working machines and the top swing body are operated by the supplied working oil.
In this case, when a swing operation quantity is increased in order to suddenly rotate the top swing body through an operation of a swing operation unit, a swash plate of a hydraulic pump is controlled so as to discharge a flux corresponding to a swing operation quantity. As a result, a considerable flux is discharged from the hydraulic pump. However, the top swing body has a large rotational inertia and therefore, a swing speed thereof is not suddenly increased in proportion to the flux discharged from the hydraulic pump but is slowly increased. Therefore, the whole flux discharged from the hydraulic pump cannot be used for the driving of the swing motor, such that the pressure of the working oil is increased and the pressure of the increased working oil exceeds pressure of a swing relief.
In this case, hydraulic parts may be damaged and most flux discharged from the hydraulic pump at the early stage of swinging is discharged to a tank through a swing relief valve to increase a loss of power.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.